Potential divider for stepwise regulation of transformers



Nov'o 15, 1949 Filed June 26, 1947 P. LEYVRAZ POTENTIAL DIVIDER FOR STEPWISE REGULATION OF TRANSFORMERS 2 Sheets-Sheet l Illi Fig. 2

Nov. 15, 1949 P. LEYvRAz 2,488,418

POTENTIAL DIVIDER FOR STEPWISE REGULATION OF TRANSFORMERS Filed June 26, 1947 2 Sheets-Sheet 2 Fig@- Patented Nov. 15,V 1949 POTENTIAL DIVIDER FOR STEPWISE REGULATION OF TRANSFORMERS Pierrev Iieyvraz, Zurich, Switzerland, assigner to Maschinenfabrik Oerlikon, Zurich-Oerhkon, Switzerland, a firm of Switzerland Applicationjune 26, 1947,v serial No. 757,304 In Switzerland March 27, 1947 4:- Claims'.

In vehicles operated by single-phase alternating current', the motor voltage is generally regulated by one or more potential dividersr being connected through contactors to different' tappings of the low-voltage winding of the transformer. When the motor currents are small, one single inductive potential dividerl is generally sufficient, the current to be operated by a contactor being equal to half the total motor current. When the currents are greater, it is advantageous to divide the current into several branches in order to reduce the current to be operated by each one of the contactors.

The object of the invention is to provide a potential divider for single phase alternating current in which a closed iron core is used which is provided with four parallel legs which have each two coils mounted thereon, all eight coils' of which are similar and each pair of which forms a branch circuit leading from one transformer tap over contactors to a common conductor leading to one terminal of a motor, the two coils of each branch circuit being mounted on different legs of the iron core.

In the drawings:

Fig. l illustrates diagrammatically a wiring system of a conventional potential' divider,v

Fig. 2 illustrates diagrammatically and by'way of example a wiring system of a potential divider of the present invention,

Fig. 3 illustrates a switching table of the potential divider of Fig. l, and the Figs. 4 and 5 illustrate flux courses for different steps.

Referring to the drawings, Fig. l illustrates a conventional potential divider in which the total current is divided into four branches. This is accomplished by two small potential dividers 50 and one large potential divider 5I, the large divider having double the power of one of the smaller ones. The contactors Il to 22 are controlled in such a manner that at each running step there are closed four contactors. Fig. 3 shows the switching table in which the contactors closed at each of the running steps l to 9 are indicated by an X. At the odd numbered steps, for instance, step 3, the two contactors I3' and I4 connected with the tap 24 are closed and the two contactors I and I6 connected to the tap 25 are also closed. At the even numbered steps, for instance, step 4, only the contactor I4 is closed which is connected with the tap 24, and the two contactors i5 and i3 connected with the tap 25 are closed as is the contactor Il' which is connected with the tap Iwith the terminal 33.

dividers are, as a rule, of the core type with two cores. One draw-back of this arrangement of wiring consists in the diferent sizes of the potential dividers and inthe number of cores which haveV a comparatively high total weight.

The present invention avoids these drawbacks by adopting a potential divider of the four-legged core type, carrying eight similar coils, each pair of which forms a branch leading from one contactor to the commonl junction point. The two coils of each branch are arranged on two different legs in such a way that the currents in the four branches are exactly equal.

Fig. 2 shows an example of execution of the invention. The eight coils 34 to 4l mounted on the four legs 42, 43, 44 and 45 are connected in' such a manner that the coils 34 and 35 are a1'- ranged in series and form a branch support. In similar manner the coils 36 and 31 are arranged in series, the coils 38 and 39-are arranged in series and the coils 43 and 4| are arranged in series and form each a branch circuit and these branch circuits are connected on one end with the terminals 29, 3D, 3| and 32and at the other end they are connected to a common terminal 33. Each of these branch circuits carries a working current of the same magnitude and the sum of these currents is consumed by the single phase motor 48. Instead of one motor 48 as shown in Fig. 2 there may be provided a plurality of motors and the same may be arranged in series,

in series parallel or in parallel. The coils 34 to 4I are connected in such a manner that on each leg one coil produces ampere turns in one direction while the other coil on the same leg pro-` duces the same number of ampere turns in the other direction, so that, neglecting the magnetizing current the ampere turns compensate each other. The coils of all four branches are cyclic coupled with each other. The coil 35 connected to the terminal 23 reacts with the coil 38 connected to the terminal 3l and the coil 39 in series with the coil 38 reacts with the coil 36 connected to the terminal 3i). The second coil 31 connected to the terminal 30 reacts with the coilv 40 connected to the terminal 32 and the other coil 4I reacts with the coil 34 which latter is arranged in series with the coil 35 and is connected circuits are alike during the operation of the rthis arrangement of the. coils insures that the currents in all four branch 3 as indicated in the table of Fig. 3 or in other words they may be controlled in the same manner as shown in the control system of Fig. 1.

Fundamentally, the four branch circuits connected to the terminals 29 to 32 may be connected in any desired manner with the two or three simultaneously used taps 23 to 28 of the secondary winding 49 of the transformer. However, there is a possibility that the inductions produced in the legs of the closed iron core will be higher as is absolutely necessary. The smallest inductions in the legs is produced when the two coils of each individual leg are arranged in two branch circuits which do not lead to the same transformer tap. The wiring arrangement illustrated in the Figs. 2, 4 and 5 fulfills this desirable condition. For instance, the coil 34 on the leg 42 is arranged in the branch circuit leading to the terminal 29 and the latter is connected by means of the contactors I3, I'I and 2I to the transformer taps 24, 26 and 28, while the coil 4| arranged on the same leg 42 belongs to the branch circuit leading to the terminal 32 which by means of the contactors I2, I3 and 2U is connected to the taps 23, 25 and 2l of the transformer. The coils on the other legs 43, 44 and 45 are arranged in similar manner so that each one is connected to the transformer taps 24, 26 and 28 and the other to the transformer taps 23, 25 and 21. By observing this arrangement the capacity of all coils will be as large as the total capacity of the coils in the arrangement of Fig, l.

The Figs. 4 and 5 illustrate the direction of the magnetic fluxes in the different steps whereby it is assumed that the control system as shown in Fig. 3 is employed. Fig. 4 discloses the closing of the running step 2 in which the contactors I2 to I are closed. The branch circuit identified by the terminal 32 is connected to the tap 23; the branch circuits identified by the terminals 2S and 30 are connected to the tap 24 and the branch circuit identied by the terminal 3l is connected to the tap 25. The direction of the magnetic flux is indicated by the two parallel hatched lines. This flux induces in one branch circuit a voltage which is equal to the difference in potential between two transformer taps. In the branch circuit connected to the terminal 3l the coil 38 in the direction of its winding is penetrated by the ilux in the leg 44 and the coil 39 is penetrated by the iiux in the leg 43 also in the direction of its winding so that as a result the voltages induced in the two coils 38 and 39 are added to each other. The sum of these potentials constitutes the voltage of the branch circuit connected to the terminal 3| and this voltage is equal to the voltage between the two transformer taps. In the branch circuit connected to the terminal 32 the voltage is of the same magnitude so that the two branch circuits connected to the terminals 3| and 32 when added together are equal to the potential between the taps 23 and whereby the one connecting point 33 shows the saine potential as the tap 24.

The coil 34 of the branch circuit connected to the terminal 29 is penetrated by the ux in the leg 42 in the direction of its winding. However, the direction in the second coil of the same branch circuit is opposite, so that the induced voltage in this particular branch circuit is zero. The same holds for the two coils 3E and 31 of the branch circuit connected to the terminal 30 so that the voltage at the terminal 3D is equal to the voltage on the terminal 24.

The Fig. 5 illustrates the condition when the running step 3 is connected or operative and in which the contactors I3 and I4 connected with the tap 24 are closed and in which also the contactors I5 and IB are closed which are connected with tap 25. In this case the magnetic fluxes in the legs 42 to 45 are only half as large as they were at the preceding running step 2. The four branch circuits all carry the same voltage which is equal to half the voltage between two transformer taps so that the potential of the common connecting point lies in the center between the two taps 24 and 25.

At the running step 2 as shown in Fig. 4 and at all other even numbered steps the magnetic flux in the legs 42 and 43 are directed opposite each other so that the flux in the center portion of the yoke 46 will be zero. At the running step 3 as shown in Fig. 5 and all other odd numbered steps the magnetic iiux in the legs 42 and 43 are directed in the same direction so that in the center portion of the yoke 4B the sum of the magnetic flux is established. Since, however, in these last cases the flux in the legs is only half as large as they create at the step 2 the flux in the center portion of the yoke 4B will be of the same magnitude as the flux in the legs produced at the running step 2. This novel arrangement of the present invention, therefore, has the advantage that all cross sectional areas of the mag netic circuit may be made of the same size and that the entire cross sectional area of this magnetic system is fully exploited.

This advantage, however, will not be obtained when any desired succession of the legs 42 to 45 is selected. For instance, by a parallel arrangement of the legs 42, 44, 43, 45 the direction of the magnetic flux at the running step 2 in the legs 42 and 44 would be in the same direction so that in the center portion of the yoke the magnetic flux would be twice as large and, therefore, it would be necessary to double the cross section at this portion of the magnetic path. In order to rprevent these conditions which would unnecessarily increase the weight of the iron core, the following condition has to be fullled. The two coils of each branch circuit have to be placed on opposite sides of the symmetry axis 4T of the voltage divider.

The advantages of the wiring in accordance with the invention as compared with known arrangements of wiring, comprise consequently simpler construction, since all coils and cores are alike, as well as less total weight, since the rpower is distributed over fewer cores. In addition to that, the requirements and losses in connection with wattless current are less than with the known wiring arrangements.

What I wish to secure by Letters Patent is:

1. The combination with a supply transformer having taps providing different voltages, of a closed iron core having four parallel legs, each of which having two coils mounted thereon, all of said coils being similar, and means including contactors for arranging said coils in groups of two serially in branch circuits connecting said taps with a common conductor leading to one terminal of a single phase alternating current motor, the coils in each group being positioned on diierent legs of said iron core.

2. The combination with a supply transformer having taps providing different voltages, of a closed iron core having four parallel legs, each of which having two coils mounted thereon, all of said coils being similar, and means including contactors for arranging said coils in groups of two serially in branch circuits connecting said taps with a common conductor leading to one terminal of a single phase alternating current motor, the coils in each group being positioned on different legs of said iron core, and the coils mounted on the same leg being connected to different taps of said transformer.

3. The combination with a supply transformer having taps providing different voltages, of a closed iron core having four parallel legs, each of which having two coils mounted thereon, all of said coils being similar, and means including contactors for arranging said coils in groups of two serially in branch circuits connecting said taps with a common conductor leading to one terminal of a single phase alternating current motor, said motor being supplied with current by said branch circuits and four simultaneously closed oontactors, the coils in each group being positioned on different legs of said iron core.

4. The combination with a supply transformer having taps providing different voltages, of a closed iron core having four parallel legs, each of which having two coils mounted thereon, all of said coils being similar, and means including contactors for arranging said coils in groups of two serially in branch circuits connecting said taps with a common conductor leading to one terminal of a single phase alternating current motor, the coils in each group being positioned on different legs of said iron core, and on opposite sidesI of the symmetry axis of the closed iron core.

PIERRE LEYVRAZ.

REFERENCES CITED The following references are of record in the Ille of this patent:

UNITED STATES PATENTS Name Date McNairy Apr. 1, 1941 Welch, Jr. Sept. 19, 1944 Number 

